How certain of someone’s guilt do we need to be before we put them to death?

In eight days, the state of Georgia is slated to execute Troy Davis, convicted of killing Mark Allen MacPhail, a Savannah police officer. It’s the fourth time Davis has been slated to die. Each of the prior three times, legal issues have resulted in stays or delays. The Supreme Court has repeatedly heard – and declined to hear – arguments on the case. In the fall of 2008, Davis came within two hours of being put to death.